The field of electrochromics is extensive and has been developing over about the last forty years. In one application, an electrochromic coating is used for controlling the amount of light and heat passing through the window based on a user-controlled electrical potential that is applied across the optical stack of the electrochromic coating. An electrochromic coating can reduce the amount of energy used for room heating and/or air conditioning, however this energy benefit is dependent on the efficiency of the electrochromic device. By switching between a clear state having an optical transmission of about 60-80% and a colored state having an optical transmission of between 0.1-10%, both energy flow into a room through a window and privacy provided by the window can be controlled. The amount of glass used for various types of windows, such as skylights, aircraft windows, residential and commercial building windows, and automobile windows, is on the order of one billion square meters per year. Accordingly, the potential energy saving provided by electrochromic glazing is substantial. See, for example, Solar Energy Materials and Solar Cells, (1994) pp. 307-321.
A conventional electrochromic cell generally is structured as follows: a substrate, a transparent conductive layer, a counter electrode, an electrolyte, an electrochromic layer, and a transparent conductive layer. Conventional cathodic materials, commonly referred to as “electrochromic electrodes,” have included tungsten oxide WO3 (most common), molybdenum oxide MoO3, niobium oxide Nb2O5, among others. Anodic materials, commonly referred to as “counter electrodes,” include nickel oxide NiO, tungsten-doped nickel oxide, and vanadium oxide (V2O5), among others. The electrolyte materials exhibit poor electron conduction, but good ion conduction. Examples of ion layer materials include silicon dioxide SiO2, titanium oxide TiO2, aluminum oxide Al2O3, and tantalum oxide Ta2O5.
Various types of transparent conducting thin films have been employed for the first and second transparent conducting layers, such as, indium tin oxide (ITO), which is the most commonly used material. Other thin oxide layers have also been used, such as fluorine-doped tin oxide, antimony-doped tin oxide, aluminum-doped zinc oxide, and fluorine-doped zinc oxide. Regardless which thin film is used, conductivities of less than about 20 Ohms/□ are needed in order to produce a uniform voltage between the two conductive layers across the conductive layers.
At the anode, the following reaction takes place:Metal Oxide or Polymer or Organic Molecule (Colored)+xM++xe−⇄Metal Oxide or Polymer or Organic Molecule (Transparent).
At the cathode, the following reaction takes place:Metal Oxide or Polymer or Organic Molecule (Transparent)+xM++xe−⇄Metal Oxide or Polymer or Organic Molecule (Colored).in which M is H+, Li+ or Na+, e is an electron, and x is an integer.
In operation, a voltage of between −5 and +5 volts is applied between the first and second conducting layers and causes reversible migration of ions between the anode and cathode resulting in the above oxidation-reduction reactions that change the absorption of the cathode, anode, or both. The electrolyte conducts ions between the materials. In a device without shorting in the electrolyte between the two conductive layers, the device resistance is high and is primarily due to the resistance of the electrolyte.
Laser irradiation is capable of ablating materials by several mechanisms, with the primary mechanism being thermal vaporization. Each material has a different ablation threshold for each wavelength of laser light. The ablation threshold is a function of material properties and absorption of the wavelength used. Ablation threshold and fluence are described in units of energy per unit area. In order to adjust the fluence, the power output of the laser, the duration of the exposure, and/or the spot size of the incident light can be controlled. To adjust the duration of exposure, the speed of the laser scribe process can be adjusted. In the case of pulsed lasers, the repetition rate and pulse width can also control the duration of laser light exposure. Due to these attributes of laser processing, reducing the ablation threshold reduces the fluence for a desired process, thereby permitting the process to be performed using less energy, at a faster scribe speed, or both. This is a desirable situation for processing speed and process costs.